P4 port in uPSD33XX can work in 4 modes, capture,timer, toggle mode and PWM, only in timer mode(the clock of timer is from OSC), no any pins need to be configed as input or output, for example , in capture mode , input pins are needed, in toggle and pwm modes, outpout pins are needed, so I think all pins of P4 port may be configed as GPI/O when timer mode is working.

P4 is shared with the PCA (programmable counter array) see the data sheet
www.st.com/stonline/books/pdfdocs/9685.pdf I can't see any reference to TCM0 and TCM1, but any P4 pin that you're not using as cex0 cex1 cex2 or ec1 can be used as gpio.